Notes app problems since importing Evernote files

A few months ago I imported Evernote files to my Apple Notes app on my Mac. Since then it has been extremely slow in responding to commands. Additionally, the Notes app on my connected iPad and iPhone has never fully synced since the import of the Evernote files. The iCloud header in the folder structure on the latter two devices now permanently has the circling icon indicating continuous communication with iCloud. Does anyone have suggestions on how to correct this issue? Thank you.